Surely there are some nicely slick lubricated ones which dont rely on dry cogs grinding against each other ?

I've opened up servos and greased the plastic gears, but it doesn't change the sound level much. Metal geared servos might be quieter, but I don't have any to check.

What is probably wanted would be helical geared servos; I am not sure whether metal or plastic would make the difference, my gut feeling would be on plastic, though. I would hazard a guess that the noise of most servos comes from using a long spur gear train with straight teeth and a high-speed motor. If you could find a servo that used helical gearing, a slower motor, and a first-stage reduction using a worm gear, you would probably see a vast reduction in noise.

Just don't expect it to be cheap (if it exists at all).

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.